Micro-strip and stripline junction circulators

ABSTRACT

A junction circulator having (one) microstrip or (two) stripline discs, or other geometries of ferrimagnetic material or in combination with non-ferrimagnetic insulating materials, spaced between a conducting ungrounded center plate and (one) microstrip or (two) stripline conducting ground plates. Three or more center conductors are connected to the center or ungrounded plate at points having generally equal angles in degrees apart. A magnetic biasing field is applied parallel to the Z axis of the ferrite discs. The bandwidth of the circulator is increased by having each center conductor tapered so as to increase in width as each center conductor approaches the center plate.

United States Patent 1m Wainwright l l MICRO-STRIP AND STRIPLINE JUNCTION CIRCULATORS [76] Inventor: Richard A. Wainwright, 9704 Kensington Pkwy., Kensington, Md. 20795 22 Filed: Dec. 23, 1971 211 App]. No.: 211,238

[ Sept. 11,1973

Primary Examiner-Paul L. Gcnsler AnorneyMorris Kirschstein et al.

[57] ABSTRACT A junction circulator having (one) microstrip or (two) stripline discs, or other geometries of ferrimagnetic material or in combination with non-ferrimagnetic insulating materials, spaced between a conducting ungrounded center plate and (one) microstrip or (two) stripline conducting ground plates. Three or more center conductors are connected to the center or ungrounded plate at points having generally equal angles in degrees apart. A magnetic biasing field is applied parallel to the Z axis of the ferrite discs. The bandwidth of the circulator is increased by having each center conductor tapered so as to increase in width as each center conductor approaches the center plate.

4 Claims, 7 Drawing Figures PAIENIEDSEPI 1 ma 3,758,878

sum 10F 2 RICHARD A Mama/yaw PATENIEDSEI'I um 3,758,878

' sum 2 BF 2 I FIG. 2 PRIOR ART F 7 INVENTOR.

H Emma A. WWW/RIGHT MICRO-STRIP AND STRIPLINE JUNCTION CIRCULATORS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to junction circulators and more particularly to microstrip and stripline circulators having an increased bandwidth over the type of junction circulator which has uniform width ungrounded conductors.

2. Description of the Prior Art The theory and operation of junction circulators are described in Linear Ferrite Devices for Microwave Applications by Aulock & Fay, Supp. 5, 1968, pages 116 to 129.

The Y-junction circulator described in the above reference and in U.S. Pat. No. 3,355,679, has two ferrite discs spaced between a conducting center plate and two conducting ground plates. These devices also may have three stripline center conductors connected to the center plate at points 120 apart, and a magnetized field is applied parallel to the Z axis of the ferrite discs. Eachof the center conductors is of uniform width. For a given desired isolation between between adjacent conductors, it is often necessary to obtain a working bandwidth which is greater than the bandwidth of present devices which use approximately one or more quarter wavelength long center conductors having uniform width over approximately one or several quarter wavelengths. It has been theorized that center conductors having uniform widths tend to cause an abrupt field discontinuity between the conductor and the center plate at the junction therebetween, which tends to limit the bandwidth of the device. I

SUMMARY OF THE INVENTION 1. Purpose of the Invention It is an object of this invention to provide for an improved junction circulator having increased bandwidth for a given isolation between adjacent conductors by varying the shape of the conductors.

It is another object of this invention to provide for a junction circulator which has a decrease in the field discontinuity at the junction between the center plate and each center conductor.

Other objects of the invention will in part be obvious and in part be pointed out herewith.

2. Brief Description of the Invention According to a broad aspect of the invention, there is provided a junction circulator including a conducting ungrounded plate, and, first or first and second ferrite discs positioned on one or opposite sides of said center ungrounded plate, first or first and if used second ground plates positioned adjacent to respective first and second discs, and three or more stripline or microstripline center conductors connected to said ungrounded center plate, each of said center (ungrounded) conductors being radially spaced generally equally in degrees apart from one another, the improvement comprising that each of said center conductors be so tapered that the width thereof is greater at a point proximal to said center plate than at a point distal from said center plate to increase the bandwidth of operation of said circulator.

A feature of the invention providesthat each of the center conductors is linearly tapered, and may or may not be stepped as to width and/or serrated.

Another feature of the invention provides that each of the center conductors is exponentially tapered.

Another feature of the invention provides that each center ungrounded conductor may be stepped in width being wider at points proximal to said center plate than at points distal from same.

A further feature of the invention provides that each of the center conductors include a main portion and first and second serrated portions, each serrated portion may extend from the sides of the main portion.

A still further feature of the invention provides that the main portion of each of the center conductors may be of uniform width stepped or uniformly tapered and each of the serrated portions is tapered as to length and/or separation.

In still another feature of the invention, each serrated portion has a plurality of teeth and the distance between each tooth may increase in the direction distal from the center plate.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings in which are shown various possible embodiments of my invention,

FIG. 1 shows an exploded perspective view of a stripline Y-junction circulator;

FIG. 2 shows an exploded perspective view of a micro-stripline Y-junction circulator;

FIG. 3 is an enlarged top view of the center plate and three stripline micro-stripline conductors for the Y- junction circulator shown in FIGS. 1 and 2;

FIG. 4 is an enlarged top view of the center plate and three ungrounded conductors for the Y-junction circulator, wherein the conductors are shown linearly tapered, step tapered around a linear profile and serrated around a linear profile;

FIG. 5 is a top view of the center plate and three ungrounded conductors for a Y-junction circulator, wherein the conductors are exponentially tapered;

FIG. 6 is a top view of the center plate and three conductors for a Y-junction circulator wherein the conductors are serrated (only one leg is shown as serrated in FIG. 6), these serrations being tapered in length and or spacing; and

FIG. 7 shows an additional outline of taper which may be used with or without serrations or step tapered around a smoothly tapering profile.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A standard Y-junction stripline circulator is shown in FIG. 1 and a standard Y-junction micro-stripline junction circulator is shown in FIG. 2. Center ungrounded plate 10 is shown disposed between ferrimagnetic discs 12 and 14, in FIG. I and above ferrimagnetic disc 14 in FIG. 2. The discs in FIG. 1 are in turn disposed between ground plate conductors l6 and 18 and in FIG. 2 disc 14 is disposed above ground plate conductor 18. Center plate 10 has in this case, but is riot limited to, three stripline conductors 20, 21 and 22 attached to the periphery thereof, wherein each conductor may be and are in this case radially spaced degrees apart from each of the adjacent conductors. Ground plates 16 and 18 can be made of any suitable conductive material, such as copper, and center plate 10 along with conductors 20, 21 and 22 can also be made of suitable conductive material, such as copper, gold, etc. Although not shown, center plate 10 and conductors 20, 21 and 22 can be formed on a substrate such as an aluminum doped yttrium iron garnet substrate, using standard printed circuit techniques. The center plate controls the center frequency of operation. The length of conductors 20, 21 and 22 is designed so as to be in the general range of one or more quarter wavelengths at the center frequency desired and the width properties of the center conductors is selected in accordance with the characteristic impedance and impedance vs. frequency properties required for impedance-mating purposes.

FIG. 3 shows atop view of center plate 10 and center conductors 20, 21 and 22 wherein these center conductors are of uniform width and have in this example a characteristic impedance of approximately 28-34 ohms and there is db of isolation between two of the adjacent center conductors, and, generally negligible loss or isolation between the other two, which isolation depends on the polarity orientation of the magnetic biasing field.

As shown in FIG. 4, center conductors 20, 21 and 22 are so linearly tapered that the width of each is greater at a point proximal to center plate 10 than at a point distal from center plate 10. Conductors 20, 21 and 22 in this instance illustrate three distinct types of linear tapers. Conductor 20 has a center section 23 of uniform width and serrated portions 24 extending from opposite sides thereof, wherein the outer edges of the serrated portions has a linear taper. Conductor 21 consists simply of two tapered edges. The outer edges of conductor 22, however, has a multiplicity of uniform steps 25 which effectively provide a linear taper. It should be noted, of course, that all three conductors generally can have just one type of the linear tapers described above. In this example, the amount of taper is determined by making the width of each conductor at the approximate means distance between the center plate and the ends of each conductor so wide as to still have a mean characteristic impedance of approximately 28-34 ohms at the operating center frequency, while each conductor is made approximately in the range of an integral multiple of quarter wavelengths long for the selected operating center frequency. Generally, during device development, the taper is made larger than required and is incrementally reduced until the mean characteristic impedance is obtained for the desired isolation required, which isolation, in this example, is 20 db. These examples in general apply to 50 ohm nominal terminal impedances, but any and all real values can be obtained depending on design parameters including cases of unequal terminations on any or all of the lines.

As shown in FIGS, conductors 20, 21 and 22 are exponentially tapered. By way of example only, the exact shape of this taper is determined as follows. Radial line 26 is drawn so as to extend midway between conductors 20 and 21, and radial line 28 is drawn so as to extend midway between conductors 21 and 22, and likewise radial line 30 is drawn so as to extend midway between conductors 22 and 20. Arcs are then drawn tangent to center plate 10 from a point along each of lines 26, 28 and 30 so that the characteristic impedance of each conductor would be in this example 38 to ohms at the most distal point from the center plate, which point is required for each conductor to be generally in the neighborhood of one quarter wavelengths long for the operating frequency of the Y-junction circulator.

However, what usually happens in this example is that due to the shape of the exponentially tapered conductors, the resonant frequency of center plate 10 is low by about I0 percent to 12 percent on the first pattern cut. In order to compensate for this, the areal size of conductor 10 is reduced sufficiently to increase the center frequency so as to place it at its desired operating value. Then arcs are again drawn from respective lines 26, 28 and 30, tangent to the periphery of the new center plate so that the approximate distal one or more quarter wavelengths point for each of the conductors will have a characteristic impedance of approximately 38 to 40 ohms. This time however the center frequency of center plate 10 will usually be within from 1 percent to 2 percent of the desired value and if this error is too great, the procedure can be repeated. This iterative process is believed to be desirable because of variations in materials properties as manufactured.

In the embodiment shown in FIG. 6, conductors 20, 21 and 22 are exponentially tapered in the manner described with reference to FIG. 5. The conductors are then subjected to metal removal processes so as to have the serrated shape, as shown in FIG. 6. In this particular example the main portion 32 of each conductor is of uniform width (although it need not be, since there are situations where one or more width steps or a taper in the main line widths (32) is desirable) and has a characteristic impedance of 50 ohms but in the general case is determined by design parameters. Each serrated tooth 34 can be separated from the adjacent serrated tooth by a distance which increases from the center plate to the end of each conductor. The change in separation'between each-tooth can increase geometrically, for example, so that the first change in separation is 5 mils, the second change is IOmils, the third change is 20 mils, and the fourth change is 40 mils, and the fifth change is mils. Therefore, if the separation between the first tooth and the center plate is I0 mils, and the separation between the first tooth and second tooth is 15 mils, and between the second tooth and the third tooth is 25 mils, and between the third tooth and the fourth tooth is 45 mils, and between the fourth tooth and the fifth tooth is mils, and between the fifth tooth and the sixth tooth is mils. In this example, the width of each tooth was made 56 percent (microstrip characteristic impedance approximately 50 ohms on microstrip substrate having a dielectric constant of approximately 15) the thickness of the aluminum doped yttrium garnet substrate used, and, in this example the substrate was mils thick.

As shown in FIG. 7, conductors 20, 21 and 22 can have a taper which follows a prescribed mathematical formula. Each conductor may have the solid form of conductor 21, the serrated form of conductor 20 or the stepped form of conductor 22. It should be noted that the main portion 36 of serrated conductor 20 may or may not be of uniform width.

It should be noted that for a given isolation of 20 db between adjacent conductors and a given center frequency of f the pattern shown in FIG. 3 (uniform linear tapes) in general yielded a bandwidth which was 30 percent of f,,; the pattern shown in FIG. 4 yielded a bandwidth which was approximately equal to 40 percent of f,,; the pattern shown in FIG. 5 yielded a bandwidth of approximately 47 percent to 48 percent of f,,; and the pattern shown in FIG. 6 yielded bandwidth of approximately 54 percent to 58 percent of f,,. It thus seems therefore that by appropriately tapering the center conductors, for a given frequency and desired isolation, the bandwidth increases over the bandwidth which is obtainable when using uniform width nontapered center conductors in a y-junction circulator.

It is thus seen that there is provided stripline and microstrip Y-junction circulators which achieve the several objects of the invention and are well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein described, or shown in the accompanying drawings are to be interpreted as illustrative and not in a limiting sense.

Having thus described the invention, there is claimed as new and is desired to be secured by Letters Patent:

1. A junction circulator including a conducting center plate, at least a first ferrite disc having one surface positioned adjacent one side of said center plate, at least a first ground plate positioned adjacent the opposite surface of said first disc, at least three center conductors connected to said center plate, each of said center conductors being equally and radially spaced apart from one another. a magnetic field in communication with said conductors, the improvement comprising that each of said center conductors is provided with linearly tapered serrated edges such that the width thereof is greater at a point proximal said center plate than at a point distal from said center plate thereby increasing the band width of said circulator.

2. A junction circulator according to claim 1 wherein each of said center conductors is approximately exponentially tapered.

3. Ajunction circulator according to claim 2 wherein each of said center conductors includes a main portion and first and second serrated portions, each serrated portion extending from opposite sides of said main portion.

4. A junction circulator according to claim 3 wherein each serrated portion has a plurality of teeth and the distance between each tooth increases in the direction distal from said center plate. 

1. A junction circulator including a conducting center plate, at least a first ferrite disc having one surface positioned adjacent one side of said center plate, at lEast a first ground plate positioned adjacent the opposite surface of said first disc, at least three center conductors connected to said center plate, each of said center conductors being equally and radially spaced apart from one another, a magnetic field in communication with said conductors, the improvement comprising that each of said center conductors is provided with linearly tapered serrated edges such that the width thereof is greater at a point proximal said center plate than at a point distal from said center plate thereby increasing the band width of said circulator.
 2. A junction circulator according to claim 1 wherein each of said center conductors is approximately exponentially tapered.
 3. A junction circulator according to claim 2 wherein each of said center conductors includes a main portion and first and second serrated portions, each serrated portion extending from opposite sides of said main portion.
 4. A junction circulator according to claim 3 wherein each serrated portion has a plurality of teeth and the distance between each tooth increases in the direction distal from said center plate. 